The present invention relates to a method of forming multilayered wiring, to be used when manufacturing an integrated circuit device such as an LSI.
In a conventional method of precisely forming a resist pattern for a contact hole to be formed in an interlayer insulating film, a reflection preventing film such as TiN is deposited on the surface of an underlie wiring layer prior to forming an interlayer insulating film covering the underlie wiring layer (for example, refer to Japanese Patent Laid-open Publication No. 1-266746). FIGS. 3 to 4 illustrate an example of a conventional multilayered wiring forming method of this type.
In the processes illustrated in FIG. 3, TiN, Al alloy (e.g., Al-Cu), and TiN are sequentially deposited on an insulating film 2 such as SiO.sub.2 covering the surface of a semiconductor substrate 1 such as Si. These layers are patterned to form a wiring layer 3 made of a TiN layer 3a, an Al alloy layer 3b, and a TiN layer 3c. The TiN layer 3a is used as a barrier layer, and the TiN layer 3c directly deposited on the Al alloy layer 3b is used as a reflection preventing film. As the TiN layer 3a, Al alloy 3b, TiN layer 3c are deposited on a flat surface of the semiconductor substrate, the TiN layer 3a, 3c and the Al alloy layer 3b also have flat surfaces thereon.
Next, an interlayer insulating film 4 such as phospho-silicate glass (PSG) or plasma enhanced CVD SiO.sub.2 is formed on the wiring layer 3 while covering the insulating film 2. After smoothing the surface of the interlayer insulating film 4, a resist layer 5 is formed. The resist layer 5 is exposed and developed to form an opening corresponding to a desired contact hole. Using the resist layer 5 with the opening as a mask, a contact hole 6 is formed in the insulating film 4 by a selective etching process. In this etching process, the TiN layer 3c just under the contact hole 6 is etched to prevent an increase of the contact resistance.
The reflection preventing Film such as the TiN layer 3c covering the surface of a high reflectance wiring layer such as Al alloy and Al prevents light from being reflected from the wiring layer surface during the lithography process. It is possible to prevent a distortion or enlargement of an opening pattern off the resist layer which might otherwise be caused by the light reflected from the wiring layer surface.
In the processes illustrated in FIG. 4, after the resist layer 5 is removed, a wiring material such as Al or Al alloy is deposited on the surface off the device, and patterned to form a wiring layer 7 which is electrically connected via the contact hole 6 to the wiring layer 3.
With the above-described method, however, when the laminated structure of the wiring layer 3 made of the TiN layer 3a, Al alloy layer 3b, and TiN layer 3c is patterned and etched using the resist layer as a mask, the etched Al alloy layer 3b is likely to have side etches, resulting in a reduced width of the Al alloy layer 3b and an increase of wiring resistance, and lowering the resistance against electromigration and stress migration.
Furthermore, a reflection preventing film such as TiN directly deposited on tile surface or a wiring layer may change the characteristics of the wiring layer, requiring a long term reliability evaluation test.